Throughout this application, various publications are referenced within parentheses. The disclosures of these publications are hereby incorporated by reference herein in their entireties.
The present invention relates to processed neural signals that encode a reach plan from a subject for use, for example, to instruct a natural limb or a reach device to carry out the reach plan.
Present day limb prosthetics are manually operated, for example by converting electrical signals from a muscle contraction into a mechanical signal to move a limb. This provides only crude control to patients having some remaining limb musculature; thus, it cannot be used by quadriplegics. Recent efforts have been directed to prosthetic limbs that can be controlled directly by a subject""s brain. It has been previously determined that the posterior parietal cortex (PPC) plays a role in motor planning, and that planned eye and arm movements are anatomically segregated in the PPC (L H Snyder, et al 1997 Nature 386: 167-170). The steps involved in the act of reaching by a limb (e.g., an arm) of a subject, comprise a reach that includes the steps of: 1) identifying the reach target; 2) planning the reach and also deciding to reach; 3) and executing the reach for the reach target. A planned reach (or reach plan) includes the second step.
The neural events associated with a visually guided reach act begin with an image of the intended reach target on the subject""s retinas and end with neural impulses to the muscles of the subject""s arm involved in executing the reach. Information about the spatial location of the reach target is initially represented in an eye-centered reference frame that the brain transforms into a limb-centered frame, in order to specify an appropriate reach command.
Information about the reach target location is encoded in visual cortical areas relative to an eye-centered reference frame. In order to execute the arm reach, this spatial information is passed through the PPC and then on to the motor cortex in the frontal lobe which receives this information of the reach target location relative to a limb-centered reference frame. In the brain, the PPC resides between the visual areas that encode spatial information and motor cortical areas that encode movement of a limb. Therefore, the PPC is anatomically positioned to play a role in transforming sensory signals into motor plans, such as a reach act.
The PPC contains several subdivisions, including the lateral intraparietal region (LIP) and the parietal reach region (PRR). The PPC contains neurons that encode an intended movement of a specific part of the body in a specific direction. In particular, a population of neurons within the parietal reach region (PRR) encode the reach plan (L H Snyder, et al 1997 Nature 386: 167-170). The role of the LIP and PRR in motor planning, such as planned saccades and planned reaches, has been previously determined by monitoring the activity of neurons in these regions in Rhesus monkeys, while the monkeys performed interleaved delayed saccade and delayed reach trials (L H Snyder, et al 1997 Nature 386: 167-170). The planned-saccades and planned-reaches are encoded separately by the LIP and the PRR, respectively. Many neurons within LIP area exhibited more neural activity when the monkey planned a saccade, while neurons within PRR exhibited more activity during a planned reach (L H Snyder, et al 1997 Nature 386: 167-170). Furthermore, the activity of the neurons within the PRR is also modulated by the current eye position and the initial hand position of the subject, or the so-called gain field effect (D. Zipser and R A Andersen 1988 Nature 331: 679-684).
Researchers have proposed that each subdivision within the brain encodes its respective movement in the coordinate frame appropriate for making the movement (Colby, Neuron 20: 15 (1998); Rizzolatti et al, Attention and Performance, Umilta and Moskovitch, Eds. (MIT Press, Cambridge, Mass. 1994), vol. 15, pp 231-265). This proposal predicts that the reach target location will be encoded in limb-centered coordinates in the PRR. Surprisingly, the results of the experiments described below show that reach plan-encoding neurons in the PRR encode reach target locations in eye-centered coordinates.
The present invention provides processed neural signals from reach plan-encoding neurons of a subject, wherein the processed neural signal encodes the reach plan relative to the eye-centered reference frame of the subject. One embodiment of the present invention provides the processed neural signal that encodes a reach target location. Another embodiment provides the processed neural signals that comprise an eye-position gain modulation. Yet another embodiment provides the processed neural signal that encodes an impending reach plan.
The present invention also provides methods for generating the processed neural signal by: acquiring the signal from an activated reach plan-encoding neuron or from a population of activated reach plan-encoding neurons; and processing the acquired neural signal or signals. One embodiment of the methods of the present invention comprises acquiring the signal from an activated reach plan-encoding neuron by detecting the neural signal with a single sensor. A preferred embodiment comprises detecting the neural signal with a multi-sensor array. One embodiment of the methods of the present invention comprises processing the signal from an activated reach plan-encoding neuron. The methods of the present invention further comprise translating the processed neural signal into a control signal that directs a desired action by the subject, wherein the desired action includes movement of: a natural limb; prosthetic limb; or computer screen pointing device.